Submarine Eruptions

Eruptions beneath the sea surface are the most common type on Earth, but are significantly underrepresented in the historical record. Submarine eruptions display characteristics that differ from their on-land equivalents. Submarine lava flows are emplaced by incremental extrusion of lobes that are rapidly chilled in contact with the water, forming structures known as pillow lavas. Explosive fragmentation of lavas forms thick fragmental deposits known as hyaloclastites. Deep-sea submarine eruptions are common along mid-ocean ridges, where an estimated 75% of Earth's magmas erupt. Shallow submarine eruptions can produce explosive columns of steam and ash, known as Surtseyan eruptions from the new island Surtsey formed off the coast of Iceland in 1967. Explosive submarine eruptions often produce large amounts of pumice, which can form long-lived rafts of floating pumice carried long distances from the volcano by ocean currents. Lava flows entering the sea can cause explosions that create cones of ash and debris that resemble cinder cones, although they were formed from rootless vents not connected to a volcanic conduit.

Krakatau

A dark, ash-laden cloud is ejected from a submarine vent at Anak Krakatau (Child of Krakatau) on June 12, 1930. A white steam column rises above a pyroclastic-surge that travels horizontally along the sea surface in a radial direction from the vent. "Base surges" such as these are a common phenomenon of submarine eruptions. The first eruptions of Anak Krakatau to breach the surface were seen in December 1927.

Myojinsho

An explosion from the Bayonnaise Rocks submarine volcano in Japan's central Izu Islands breaches the sea surface on September 23, 1952. These cockscomb-like projections of blocks and ash are characteristic of shallow submarine explosions. This photo was taken 5 seconds after the explosion penetrated the sea surface. Five minutes later the eruption was over and the sea was again calm. The suddeness of these powerful explosions proved to be fatal to 31 people on a research vessel that sailed over the vent the following day.

Photo courtesy of Ryohei Morimoto (University of Tokyo), 1952.

Myojinsho

Steam pours from the blocky summit of a lava dome formed at Myojin-sho during a submarine eruption at the Bayonnaise Rocks volcano in 1952. This September 22 photo was taken six days after the dome began to breach the sea surface. Later that day the eruption became highly explosive, and the dome was destroyed. Three cycles of dome growth and destruction occurred until October 1953. Myojin-sho is located on the eastern rim of a 7-9 km wide submarine caldera.

Photo courtesy of Helen Foster, 1952 (U.S. Geological Survey).

Nishinoshima

A submarine explosion from Nishino-shima breaches the surface on October 9, 1973. Steam trails behind individual ejected hot blocks at the margin of the plume. Submarine eruptions began on April 12, 1973. On September 11 a new island was first seen. Lava flows began in September, and three new islands were formed, which joined together during October-November 1973 forming Nishino-shima-shinto. The new island itself was connected to the pre-existing Nishino-shima Island by wave activity after the eruption ended.